High DNA standards needed

Collecting DNA from people arrested for violent crimes sometimes leads to a big payoff for the police. That's what happened in Maryland in 2009, when DNA taken from a man arrested on assault charges, for threatening people with a shotgun, matched DNA collected six years earlier in an unsolved rape case.

Thanks to the DNA match, Alonzo King was convicted of that 2003 rape and sentenced to life without parole. On Monday, the Supreme Court upheld the conviction, saying it was fine for police to collect DNA from anyone arrested for a "serious offense," such as assault, rape, murder, armed robbery or burglary.

On its face, this case looks like a slam dunk. A guy is booked on a serious charge, and a quick, minimally intrusive DNA test shows he's implicated in a far more serious crime that has been unsolved for years. Who could object?

The fact that the Supreme Court split 5-4, in an unusual ideological mix, in deciding the case should be a clue that it's not so simple.

Collecting DNA is a deeply personal "search" that can reveal far more than a fingerprint or a mug shot. More important, testing people who have been arrested for one crime to see whether they're guilty of some other crime is the sort of suspicionless search that violates one of the most significant protections the Founding Fathers wrote into the Constitution.

Enraged by the British practice of using vague "general warrants" to justify intrusions into Americans' homes, the Founders said authorities could conduct searches only when they had probable cause to believe a crime was committed and, in most cases, had a warrant from a judge.

Imagine a slightly different context in the modern era: You're arrested for a nonviolent crime, such as bouncing a check or letting your dog off the leash in a national park. But instead of collecting DNA, authorities use your arrest as a reason to rummage through your home, with no warrant, for evidence of other crimes. Under current law, the home search would be prohibited, but the principle is the same.

That's why the Supreme Court's majority, in an opinion by Justice Anthony Kennedy, turned itself into a pretzel claiming that collecting DNA has nothing to do with checking for other crimes but everything to do with identifying arrestees.

In his dissenting opinion, Justice Antonin Scalia demolished Kennedy's logic, noting that authorities never even checked King's DNA to identify him. They knew who he was. Instead, they tested his DNA against a database of unsolved crimes.

Scalia warned of a slippery slope that could lead to the Transportation Security Administration swabbing every air traveler. But with robust safeguards, that needn't happen.

Going forward, states would do well to limit DNA tests to people who've been convicted, or at the very least to those arrested for sharply defined major violent offenses. Better yet, the court would use some future case to tighten the rules on who can be tested.

Those limits would help the nation strike an appropriate balance between crime-solving and Fourth Amendment privacy rights. And people like King could still be linked to cold cases, if authorities are a little bit more patient.